[libc++](NFC) Remove unused include caused by wrong __has_include

The parameter passed to __has_include has to be quoted by `<>` or `"`, not both.
Due to this typo, the guarded header is never included.
No problem has been reported by unconditionally skip of including, so it
would be safe to simply remove the conditionally include block.

Author: kikairoya

libcxx/src/locale.cpp

@@ -34,10 +34,6 @@
 #  define _CTYPE_DISABLE_MACROS
 #endif
 
-#if __has_include("<langinfo.h>")
-#  include <langinfo.h>
-#endif
-
 #include "include/atomic_support.h"
 #include "include/sso_allocator.h"